A location based service (LBS) provides a service based on location. The LBS may include a server-based LBS application hosted on an Internet server that is paired with a client-based LBS application hosted on an Internet Protocol (IP)-capable client device (CD), which may be stationary or mobile. The paired LBS applications may communicate with each other over the Internet. Typically, the LBS acquires a current location of the CD, and then provides an appropriate service to a consumer of the LBS, e.g., a user of the CD, based on the current location. For example, the LBS may cause the CD to display a geographical map indicating the current location, and provide audible directions that direct the user to a point-of-interest, such as a store or a restaurant in a shopping mall, etc.
Trilateration is a technique for determining a relative or an absolute location of the CD. Trilateration relies on signals that are transmitted to the CD from transmitters associated with reference points (RPs), e.g. Wi-Fi access points (APs) and beacons, having known locations. Trilateration may be used to calculate a location of the CD in a planar direction, i.e., a plane geometric location of the CD, such as its relative x, y or absolute latitude, longitude coordinates. When the CD is in a multi-story building that hosts multiple RPs dispersed across different floors of the building, the CD typically receives RP signals that originate from the different floors, including the floor on which the CD is located. Simple trilateration is insufficient to locate the CD reliably in both a planar direction and a vertical direction, e.g., to an altitude or a floor of the building.
In the multi-story environment, conventional techniques, including trilateration, that use received RP signals to detect the floor on which the CD is located, tend to be error prone, i.e., often detect an incorrect floor. This is because such techniques may simply detect the floor that originates either a strongest one of the RP signals (as received at the CD), or the most RP signals. In either case, the CD may be located on a floor different from that originating either the strongest or the most RP signals. Incorrect floor information may translate to erroneous LBS operation. For example, a map indicating a location of a CD in a multi-story building may intermittently represent the CD on incorrect floors, and thereby “jump” back-and-forth between floors depicted in the map, thus confusing the LBS consumer.
In the drawings, the leftmost digit(s) of a reference number identifies the drawing in which the reference number first appears.